Surface acoustic wave filter utilizing a layer for preventing grain boundary diffusion

ABSTRACT

In a surface acoustic wave (SAW) filter including a substrate and an electrode formed on the substrate, the electrode includes a base layer, a first metal layer made of a metal consisting of Al or consisting mainly of Al, and having a given orientation relative to the substrate, a second layer for preventing the first metal layer from migration of Al atoms occurring in vertical to the substrate, and a third layer for adjusting a thickness of the layer. In this SAW filter having an arbitrary layer thickness, the layer hardly causes grain boundary diffusion, and grains of the layer can be made fine for effective resistance to stress. Thus, in this SAW filter, the migration of the Al atoms of the electrode that is associated with the SAW propagation-induced stress imposed on the electrode is inhibited. Accordingly, the filter exhibits excellent resistance against electric power.

This Application is a U.S. National Phase Application of PCTInternational Application PCT/JP01/09303.

TECHNICAL FIELD

The present invention relates to a surface acoustic wave filterincluding an electrode, such as a comb electrode, formed on a substrate,and a method of manufacturing the filter.

BACKGROUND ART

A conventional surface acoustic wave device disclosed in Japanese PatentLaid-Open No.3-14308 includes a piezoelectric substrate and an electrodeprovided on the substrate. The electrode is constructed of anepitaxially-grown aluminum film having a certain crystal orientation.The film contains a little additive, such as Cu, Ti, Ni, Mg or Pd, whichhas excellent migration resistance, thus preventing migration.

The electrode is formed of the single-layer epitaxially grown aluminumfilm and has grain size grown as large as a thickness of the film.Consequently, if having a thickness equal to or more than a certainthickness, the electrode weakens against a stress accompanied withpropagation of surface acoustic waves, thus exhibiting a degradedresistance to an electric power. Particularly being constructed of asingle-crystal film having no grain boundary, the electrode has asub-grain boundary formed when the stress is applied for a long time.Consequently, the stress concentrates on the portion, thus weakening theelectrode against the stress accompanied with the propagation of thesurface acoustic waves.

DISCLOSURE OF THE INVENTION

A surface acoustic wave (SAW) filter with improved resistance to stressaccompanied with propagation of surface acoustic waves is provided.

The SAW filter includes a substrate and an electrode provided on thesubstrate. The electrode includes a metal layer having a thickness of200 nm or less and a given orientation relative to the substrate.

A method of manufacturing the SAW filter includes forming of theelectrode including the metal layer including Al, and forming of atleast a portion of an Al-diffusion-preventing layer on a side of theelectrode by sputter etching simultaneously with the forming of theelectrode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a surface acoustic wave (SAW) filter inaccordance with exemplary embodiments of the present invention.

FIG. 2 is a block diagram of the SAW filter in accordance with theembodiments.

FIG. 3 is a section of a comb electrode, an essential part of a SAWfilter of example 1 in accordance with exemplary embodiment 1 of thepresent invention.

FIG. 4 is a section of a comb electrode, an essential part of a SAWfilter of example 2 in accordance with embodiment 1.

FIG. 5 is a section of a comb electrode, an essential part of a SAWfilter of example 3 in accordance with embodiment 1.

FIG. 6 is a section of a comb electrode, an essential part of a SAWfilter of example 4 in accordance with embodiment 1.

FIG. 7 is a section of a comb electrode, an essential part of a SAWfilter of comparative example 1 in accordance with embodiment 1.

FIG. 8 is a section of a comb electrode, an essential part of a SAWfilter of comparative example 2 in accordance with embodiment 1.

FIG. 9 is a section of a comb electrode, an essential part of a SAWfilter of comparative example 3 in accordance with embodiment 1.

FIG. 10 is a section of a comb electrode, an essential part of a SAWfilter of comparative example 4 in accordance with embodiment 1.

FIG. 11 is a section of a comb electrode, an essential part of a SAWfilter of example 5 in accordance with exemplary embodiment 2 of theinvention.

FIG. 12 is a section of a comb electrode, an essential part of a SAWfilter of example 6 in accordance with embodiment 2

FIG. 13 is a section of a comb electrode, an essential part of a SAWfilter of example 7 in accordance with embodiment 2.

FIG. 14 is a section of a comb electrode, an essential part of a SAWfilter of example 8 in accordance with embodiment 2.

FIG. 15 is a section of a comb electrode, an essential part of a SAWfilter of comparative example 5 in accordance with embodiment 2.

FIG. 16 is a section of a comb electrode, an essential part of a SAWfilter of example 9 in accordance with exemplary embodiment 3 of theinvention.

FIG. 17 is a section of a comb electrode, an essential part of a SAWfilter of example 10 in accordance with embodiment 3.

FIG. 18 is a section of a comb electrode, an essential part of a SAWfilter of example 11 in accordance with embodiment 3.

FIG. 19 is a section of a comb electrode, an essential part of a SAWfilter of example 12 in accordance with embodiment 3.

FIG. 20 is a section of a comb electrode, an essential part of a SAWfilter of comparative example 6 in accordance with embodiment 3.

FIG. 21 is a section of a comb electrode, an essential part of each SAWfilter of examples 13 and 14, and comparative examples 7 to 10 inaccordance with exemplary embodiment 4 of the invention.

FIG. 22 is a section of a comb electrode, an essential part of each SAWfilter of examples 15 and 16 in accordance with embodiment 4.

FIG. 23 is a section of a comb electrode, an essential part of each SAWfilter of examples 17 and 18 in accordance with embodiment 4.

FIG. 24 is a section of a comb electrode, an essential part of each SAWfilter of examples 19 and 20 in accordance with exemplary embodiment 5of the invention.

FIG. 25 is a section of a comb electrode, an essential part of each SAWfilter of examples 21 and 22 in accordance with embodiment 5.

FIG. 26 is a section of a comb electrode, an essential part of a SAWfilter of example 23 in accordance with embodiment 5.

FIG. 27 is a section of a comb electrode, an essential part of a SAWfilter of comparative example 11 in accordance with embodiment 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(Exemplary Embodiment 1)

FIG. 1 is a perspective view of a surface acoustic wave (SAW) filter inaccordance with exemplary embodiments of the present invention, and FIG.2 is a block diagram of the filter. The SAW filter is a ladder-typesurface acoustic wave filter including substrate 1 and five surfaceacoustic wave resonators each including electrode 2 formed on a topsurface of substrate 1. The resonators are coupled in a ladderconfiguration. Electrode 2 includes comb electrode 21 and reflector 22.In the embodiments of the invention, substrate 1 is a 36°-rotated Y-cutlithium tantalate substrate. In exemplary embodiment 1, a band passfilter including the comb electrode having fingers disposed by a pitchof about 0.6×2 μm and has a center frequency of 1.8 GHz.

FIGS. 3 to 6 are sections of the electrodes, essential parts ofrespective SAW filters of examples 1 to 4 in accordance withembodiment 1. FIGS. 7 to 10 are sections of electrodes of respective SAWfilters of comparative examples 1 to 4.

Electrode 102 of example 1, as shown in FIG. 3, includes first layer 4having a thickness of 20 nm formed on substrate 1.

Electrode 112 of example 2, as shown in FIG. 4, includes first layer 4having a thickness of 200 nm and second layer 5 that are stacked oversubstrate 1. Second layer 5 prevents the first layer from grain boundarydiffusion of Al atoms occurring in vertical to the substrate.

Electrode 122 of example 3, as shown in FIG. 5, includes base layer 3and first layer 4 having a thickness of 200 nm that are stacked oversubstrate 1 in this order.

Electrode 132 of Example 4, as shown in FIG. 6, includes base layer 3,first metal layer 4 having a thickness of 200 nm, and layer 5 that arestacked over substrate 1 in this order. Layer 5 prevents the first metallayer from grain boundary diffusion.

Electrode 142 of comparative example 1 is, as shown in FIG. 7, metallayer 4 having a thickness of 200 nm formed on substrate 1.

Electrode 152 of comparative example 2 is, as shown in FIG. 8, metallayer 4 having a thickness of 250 nm formed on substrate 1.

Electrode 162 of comparative example 3, as shown in FIG. 9, includesfirst metal layer 4 having a thickness of 200 nm and second metal layer5 that are stacked over substrate 1 in this order. Second metal layer 5prevents the first metal layer from grain boundary diffusion of Al atomsoccurring in vertical to the substrate.

Electrode 172 of comparative example 4, as shown in FIG. 10, includesfirst metal layer 3, i.e., a base layer, and second metal layer 4 havinga thickness of 200 nm that are stacked over substrate 1 in this order.

Table 1 shows materials for the layers, thicknesses, and methods offorming the layers of the electrodes of examples 1 to 4 and comparativeexamples 1 to 4.

TABLE 1 Number Method of Section of Base First Second Forming of LayersLayer Layer Layer Layers Electrode Example 1 1 Material — *AlZrCu — IBSFIG. 3 Thickness — 200 — Example 2 2 Material — *AlZrCu Ti IBS FIG. 4Thickness — 200 20 Example 3 2 Material Ti *AlZrCu — DCMS FIG. 5Thickness 20 200 — Example 4 3 Material Ti *AlZrCu Ti DCMS FIG. 6Thickness 10 200 10 Comparative 1 Material — AlZrCu — DCMS FIG. 7Example 1 Thickness — 200 — Comparative 1 Material — *AlZrCu — IBS FIG.8 Example 2 Thickness — 250 — Comparative 2 Material — AlZrCu Ti DCMSFIG. 9 Example 3 Thickness — 200 20 Comparative 2 Material Cr AlZrCu —DCMS FIG. 10 Example 4 Thickness 20 200 — IBS: Ion beam sputtering DCMS:DC magnetron sputtering The asterisk “*” in the “material” columndenotes a (111)-oriented layer. All the thicknesses are in nm.

As shown in Table 1, the metal consisting of Al or consisting mainly ofAl is an AlZrCu alloy in embodiment 1. The electrodes each including thebase layer and/or the second layer employs Ti except for comparativeexample 4, which employs Cr for the base layer. The layers are formed byeither ion beam sputtering or DC magnetron sputtering. Having theelectrode layers formed, the electrodes were examined by a θ−2θ X-raydiffraction method to determine orientation. Regarding the orientationof examples 1 and 2 and comparative example 2 which use the ion beamsputtering to form the electrode layers as well as examples 3 and 4which use Ti for base layer 3, only a (111) peak of Al for the AlZrCulayers was observed. It was observed that the Al alloy layer was anoriented layer having a (111)-orientation in vertical to the substrate.Regarding the other electrode layers, no peak was observed from aspecified crystal plane, and it was confirmed that they were notoriented layers but non-oriented polycrystalline layers. In the presentembodiment, the Al electrode used for the filter was designed to have alayer thickness of 200 nm. Differences in characteristics that depend onthicknesses and materials of the electrodes were adjusted by changingthe pitch of the fingers of the comb electrodes, thus providing thefilters with a center frequency of about 1.8 GHz. The electrodes werepatterned by photolithography and dry etching and thereafter diced intochips. Each one of the chips was die-bonded to a ceramic package andelectrically connected by wire bonding. Thereafter, a cover is welded toit in a nitrogen atmosphere for hermetic sealing it to provide the SAWfilter having the electrodes.

A signal of a highest frequency in a passing band, which is the weakestpoint of the ladder type filter, is applied to the filters made inaccordance with the present embodiment for a test for a resistanceagainst an electric power. The test is suspended periodically formeasuring characteristics of the SAW filter. The filter is verified asdegraded at a point where an insertion loss in the passing bandincreases by 0.5 dB or more, and a total test time between the startingof the test and the degradation is determined as a life time. In anaccelerated degradation test, an electric power and a temperature werefactors responsible for accelerated degradation. The accelerateddegradation test was conducted on the filter and includes two kinds oftests. One for determination of the life time under several appliedelectric powers with the chip surface maintained in a temperature, andthe other for determination of the life time under several temperaturesof the chip with a constant applied electric power. The Eyring model andthe results of these two tests are used to estimate the life time whenthe applied electric power and the environmental temperature are 1W and50° C., respectively. A life time of 50,000 hours was qualified as acriteria for evaluation of the resistance to the electric power. Table 2shows the estimated life time of the SAW filters having the electrodesshown in Table 1. Table 2 also shows crystal grain sizes of the AlZrCulayers of the electrodes.

TABLE 2 Crystal Estimated Crystal Estimated Grain Life Grain Life Size(nm) Time (hrs) Size (nm) Time (hrs) Example 1 200 55,000 Comparative200 1,500 Example 1 Example 2 200 70,000 Comparative 250 12,000 Example2 Example 3 200 56,000 Comparative 200 5 Example 3 Example 4 200 74,000Comparative 200 1,500 Example 4

Table 2 shows that the SAW filters including the electrodes of examples1 to 4 have the estimated life time exceeding 50,000 hours, while thefilters of comparative examples 1 to 4 have the estimated life time lessthan 50,000 hours. The AlZrCu layer of each of the electrodes has thecrystal grain size substantially identical to a thickness of the layer.Although the filter of comparative example 2 has the life time less than50,000 hours, unlike the other comparative examples, the filter hasconsiderably improved resistance to an electric power. The electrode ofexample 1 defers from the electrode of comparative example 2 in athickness of the layer and the crystal grain size. A conductive layerhas a crystal grain size increasing in proportion to a thickness of thelayer. The SAW device including a single-layer electrode of the orientedlayer as the electrode layer has a thickness of the electrode of 200 nmor less and a life time exceeding 50,000 hours. With consideration givento variations in resistance to electric power, the layer preferably hasa thickness less than 100 nm. According to the above discussion, thelayer consisting of Al or consisting mainly of Al is preferably is anoriented layer having a small crystal grain size to form an electrodehaving high resistance to the electric power. Limiting the layerthickness is effective for reducing the crystal grain size.

(Exemplary Embodiment 2)

FIGS. 11 to 14 are sections of electrodes, essential parts of surfaceacoustic wave (SAW) filters of examples 5 to 8 in accordance withexemplary embodiment 2 of the present invention. FIG. 15 is a section ofan electrode of a SAW filter of comparative example 5.

Electrode 182 of example 5 is, as shown in FIG. 11, first layer 4 havinga thickness of 200 nm formed on a top of bump 7 of substrate 1.

Electrode 192 of example 6, as shown in FIG. 12, includes base layer 3formed on a top of bump 7 of substrate 1 and first layer 4 having athickness of 200 nm which are stacked in this order over substrate 1.

Electrode 202 of example 7, as shown in FIG. 13, includes first metallayer 4 having a thickness of 200 nm formed on a top of bump 7 ofsubstrate 1 and second layer 5 which are stacked in this order oversubstrate 1. Second layer 5 prevents the first metal layer from grainboundary diffusion.

Electrode 212 of example 8, as shown in FIG. 14, includes base layer 3formed on a top of bump 7 of a substrate, first metal layer 4 having athickness of 200 nm, and second layer 5 which are stacked in this orderover substrate 1. Second layer 5 prevents the first metal layer fromgrain boundary diffusion.

Electrode 222 of comparative example 5 is, as shown in FIG. 15, metallayer 4 having a thickness of 300 nm formed on substrate 1.

Table 3 shows materials for the layers, thicknesses of the layers, andmethods of forming the layers of the electrodes of examples 5 to 9 andcomparative example 5.

TABLE 3 Number Step of Method of Section of Substrate Base First SecondForming of Layers (nm) Layer Layer Layer Layers Electrode Example 5 1 20Material — *AlMgCu — IBS FIG. 11 Thickness — 200 — Example 6 2 15Material Ti *AlMgCu — DCMS FIG. 12 Thickness 20 200 — Example 7 2 15Material — *AlMgCu Ti IBS FIG. 13 Thickness — 200 20 Example 8 3 10Material Ti *AlMgCu Ti DCMS FIG. 14 Thickness 20 200 20 Comparative 1 —Material — *AlMgCu — IBS FIG. 15 Example 5 Thickness — 300 — IBS: Ionbeam sputtering DCMS: DC magnetron sputtering The asterisk “*” in the“material” column denotes a (111)-oriented layer. All the thicknessesare in nm.

As shown in Table 3, the metal layer consisting of Al or consistingmainly of Al in embodiment 2 employs an AlMgCu alloy. The electrodeseach having the base layer and/or the second layer use Ti. The layers ofthe electrodes are formed by either ion beam sputtering or DC magnetronsputtering. Having the electrode layers formed, the electrodes wereexamined by a θ−2θ X-ray diffraction method to determine orientation.Regarding the orientation of the AlMgCu layers of examples 5 to 8 andcomparative example 5, only a (111) peak of Al was observed. It wasobserved that the Al alloy layer was an oriented layer having a (111)orientation in vertical to the substrate. The filters of embodiment 2have structures identical to those of embodiment 1. The tested filterwas designed to include the Al electrode having a thickness of 300 nmand to have a center frequency of about 1.75 GHz. Differences incharacteristics that depend on thicknesses and materials of theelectrodes are adjusted by changing height of the bump of each one ofthe substrates to provide the filter with the center frequency of about1.75 GHz.

Thus, the comb electrodes of examples 5 to 8 and comparative example 5have fingers substantially at the same pitch. The electrodes arepatterned by photolithography and reactive ion etching. Mixed gasincluding BC13 and C12 is used as etching gas. Consequently, in thereactive ion etching, chemical etching with a C1* radical and a BC13*radical and sputter etching with a BC13+ ion are carried outsimultaneously for the patterning. The bump of the substrate of each oneof examples 5 to 8 is formed by controlling etching time. Subsequentlyto the patterning, the substrate is diced into chips. Each one of thechips is die-bonded to a ceramic package and electrically connected bywire bonding. Thereafter, a cover is welded in a nitrogen atmosphere forhermetic sealing, thus providing the SAW filter having the electrode.

The filters made in accordance with embodiment 2 are evaluated in thesame manner as that of embodiment 1 in resistance to an electric power.Table 4 shows an estimated life time of the SAW filters having theelectrodes shown in Table 3. Table 4 also shows crystal grain sizes ofAlMgCu layers 4 of the electrodes.

TABLE 4 Crystal Estimated Crystal Estimated Grain Life Grain Life Size(nm) Time (hrs) Size (nm) Time (hrs) Example 5 200 55,000 Comparative300 9,500 Example 5 Example 6 200 56,000 Example 7 200 70,000 Example 8200 74,000

As shown in Table 4, each of the SAW filters including the electrodes ofexamples 5 to 8 has the estimated life time exceeding 50,000 hours, acriteria, while the filter of comparative example 5 has the estimatedlife time less than 50,000 hours. The AlMgCu layer of each electrode hasthe crystal grain size substantially the same as a thickness of thelayer. As mentioned above, the Al electrode of the filter is designed toinclude the layer having a thickness of 300 nm in embodiment 2. Thesubstrate is provided with the bump as a part of the electrode, and themetal layer consisting of Al or consisting mainly of Al has a thicknessof 200 nm or less. Consequently, the electrode exhibits the sameresistance against an electric power as the electrodes of examples 1 to4 described in embodiment 1 and has the life time of 50,000 hours (thecriteria of resistance against an electric power) or more. As a result,regarding the SAW filter including an electrode including a layer havinga thickness of 200 nm or more for exhibiting desired characteristics,the substrate preferably includes a bump as a part of the electrode, andthe electrode consisting of Al or consisting mainly of Al preferably isan oriented layer having a thickness of 200 nm or less and has a reducedcrystal grain size for having an improved resistance against theelectric power.

(Exemplary Embodiment 3)

FIGS. 16 to 19 are sections of electrodes which are essential parts ofrespective SAW filters of examples 9 to 12 in accordance with exemplaryembodiment 3 of the present invention. FIG. 20 is a section of anelectrode of a SAW filter of comparative example 6.

Electrode 232 of example 9, as shown in FIG. 16, includes first metallayer 4 having a thickness of 200 nm, second layer 5, and third layer 6which are stacked in this order over substrate 1. Second layer 5prevents first metal layer 4 from grain boundary diffusion of Al atomsoccurring in vertical to the substrate, while third layer 6 is providedfor adjusting a thickness of electrode 232.

Electrode 242 of Example 10, as shown in FIG. 17, includes base layer 3,first metal layer 4 having a thickness of 200 nm, second layer 5, andthird layer 6 which are stacked in this order over substrate 1. Secondlayer 5 prevents first metal layer 4 from grain boundary diffusion of Alatoms occurring in vertical to the substrate, while third layer 6 isprovided for adjusting a thickness of electrode 242.

Electrode 252 of Example 11, as shown in FIG. 18, includes first metallayer 4 having a thickness of 200 nm formed on a top of bump 7 ofsubstrate 1, second layer 5 for preventing first metal layer 4 fromgrain boundary diffusion of Al atoms occurring in vertical to thesubstrate, and third layer 6 for adjusting a thickness of electrode 252.

Electrode 262 of Example 12, as shown in FIG. 19, includes base layer 3formed on a top of bump 7 of substrate 1, first metal layer 4 having athickness of 200 nm, second layer 5, and third layer 6 which are stackedin this order over substrate 1. Second layer 5 prevents first metallayer 4 from grain boundary diffusion, while third layer 6 is providedfor adjusting a thickness of electrode 262.

Electrode 272 of comparative example 6, as shown in FIG. 20, includesbase layer 3, first metal layer 4 having a thickness of 280 nm, secondlayer 5, and third layer 6 which are stacked in this order oversubstrate 1. Second layer 5 prevents first metal layer 4 from gramboundary diffusion of Al atoms occurring in vertical to the substrate,while third layer 6 is provided for adjusting a thickness of electrode272.

Table 5 shows materials of the respective layers, thicknesses of thelayers and methods of forming the layers of the electrodes of examples 5to 9 and comparative example 5.

TABLE 5 Number Bump of Method of Section of Substrate Base First SecondThird Forming of Layers (nm) Layer Layer Layer Layer Layers ElectrodeExample 9 3 — Material — *AlMg Ti AlMg IBS FIG. 16 Thickness — 200 10260 Example 10 4 — Material Ti *AlMg Ti AlMg DCMS FIG. 17 Thickness 10200 10 250 Example 11 3 10 Material — *AlMg Ti AlMg IBS FIG. 18Thickness — 200 10 200 Example 12 4  7 Material Ti *AlMg Ti AlMg DCMSFIG. 19 Thickness 10 200 10 200 Comparative 4 — Material Ti *AlMg TiAlMg DCMS FIG. 20 Example 6 Thickness 10 280 10 200 IBS: Ion beamsputtering DCMS: DC magnetron sputtering DCMS: DC magnetron sputteringThe asterisk “*” in the “material” column denotes a (111)-orientedlayer. All the thicknesses are in nm.

As shown in Table 5, the metal consisting of Al or consisting mainly ofAl in the present embodiment employs an AlMg alloy, and the base layerand the second layer employ Ti. The layers are formed by either ion beamsputtering or DC magnetron sputtering. Having the electrode layersformed, the electrodes was examined by a θ−2θ X-ray diffraction methodto determine orientation. Regarding the orientation of the AlMg layersof examples 9 to 12 and comparative example 6, only a (111) peak of Alis observed, and it is verified that the Al alloy layer is an orientedlayer having a (111) orientation in vertical to the substrate. Sinceeach electrode includes two AlMg layers, that is, the first layer andthe third layer, another sample including a base layer and a first layeris made under the same conditions for forming the layers for determiningthe orientation. The filters of embodiment 3 have structures identicalto those of embodiment 1. However, the filter including the Al electrodedesigned to have a thickness of 480 nm to have a center frequency ofabout 800 MHz. Differences in characteristics that depend on thicknessesand materials of the electrodes are adjusted by changing height of thebump of each substrate and changing the thickness of the third layer toprovide the center frequency of about 800 MHz. Thus, the comb electrodesof examples 9 to 12 and comparative example 6 have fingers atsubstantially the same pitch. The electrodes and the filters are made inthe same manner as those of embodiment 2.

The filters made in accordance with embodiment 3 are evaluated in thesame manner as that in embodiment 1 in respective resistances against anelectric power. Table 6 shows estimated life time of the respective SAWfilters having the respective electrodes shown in Table 5. Table 6 alsoshows crystal grain sizes of the respective AlMg layers (the firstlayers) of the electrodes.

TABLE 6 Crystal Estimated Crystal Estimated Grain Life Grain Life Size(nm) Time (hrs) Size (nm) Time (hrs) Example 9 200 53,000 Comparative280 8,800 Example 6 Example 200 55,000 10 Example 200 57,000 11 Example200 58,000 12 The crystal grain size represents the crystal grain sizeof the first layer.

As shown in Table 6, each SAW filter including the electrode of examples9 to 12 has the estimated life time exceeding 50,000 hours, while thefilter of comparative example 6 has the estimated life time less than50,000 hours. The AlMg layer (the first layer) of each electrode has acrystal grain size which is substantially the same as a thickness of thelayer. The first metal layer consisting of Al or consisting mainly of Alhas a thickness of 200 nm or less, while the Al electrode of the filter,as described above, is designed to have a thickness of 480 nm inembodiment 2. The thickness of the first metal layer is set to 200 nm orless by providing the second layer for limiting the thickness of thefirst layer, and the third layer for adjusting the thickness of theelectrode over the first layer, and/or by providing the bump as a partof the electrode to the substrate. Accordingly, the filter has highresistance against an electric power and has the life time of 50,000hours (a criteria of evaluation for resistance against an electricpower) or more. After the test, the filters of examples 9 and 10 has ahillock caused by the diffusion observed at the surface of the combelectrode besides a degraded portion of the electrode. The diffusion ofthe Al atoms is caused by degradation of the third layer adjusting thethickness. The filters of examples 11 and 12 have no hillock. Thus, thethird layer consisting of Al or consisting mainly of Al preferably has athickness of 200 nm or less. Further, a fourth layer may be provided onthe third layer to restrain the diffusion of the Al atoms from the thirdlayer. Although each filter of examples 11 and 12 and comparativeexample 6 have no hillock caused by the diffusion of the Al atoms at thesurfaces of their respective electrodes after the test, the filter has aside hillock on opposed faces of the comb electrode. The above resultsshow that, in order for the SAW filter requiring the thickness of 200 nmor more of the electrode layer for desired characteristics to have theresistance against an electric power, the second layer and the thirdlayer are preferably provided over the first layer consisting of Al orconsisting mainly of Al and having the thickness of 200 nm or less. Thesecond layer is provided for limiting the thickness of the first layer,and the third layer is provided for adjusting the thickness of theelectrode layer over the first layer. Moreover, the crystal grain sizecan be smaller by the bump as the part of the electrode provided to thesubstrate to prevent the third layer from getting thicker, and by thelayer consisting of Al or consisting mainly of Al having the thicknessof 200 nm or less.

(Exemplary Embodiment 4)

FIGS. 21 to 23 are sections of electrodes which are essential parts ofrespective SAW filters of examples 13 to 8 in accordance with exemplaryembodiment 4 of the present invention. Electrodes of respective SAWfilters of comparative examples 7 to 10 have sections each identical tothe electrode illustrated in FIG. 21.

Each electrode 282 of examples 13 and 14, as shown in FIG. 21, includesfirst metal layer 4 having a thickness of 200 nm which consists of Al orconsists mainly of Al, second layer 5, and third layer 6 that arestacked in this order over substrate 1. Second layer 5 prevents thefirst layer from grain boundary diffusion of Al atoms occurring invertical to the substrate, while third layer 6 adjusts a thickness ofelectrode 282. Diffusion-preventing layer 8 is formed on each side ofelectrode 282 to prevent first layer 4 from the grain boundary diffusionof the Al atoms and does not reach the substrate, as shown in FIG. 21.

Each electrode 292 of examples 15 and 16, as shown in FIG. 22, includesbase layer 3, first metal layer 4 having 200 nm, second layer 5, andthird layer 6 that are stacked in this order over substrate 1. Secondlayer 5 prevents first metal layer 4 from grain boundary diffusion of Alatoms occurring in vertical to the substrate, while third layer 6adjusts a thickness of electrode 292. Diffusion-preventing layer 8 isformed on each side of electrode 292 to prevent first metal layer 4 fromthe grain boundary diffusion of the Al atoms. The diffusion-preventinglayer 8 does not reach the substrate, but covers the sides of firstmetal layer 4, second layer 5, third layer 6, and a part of each side ofbase layer 3, as shown in FIG. 22.

Each electrode 302 of examples 17 and 18, as shown in FIG. 23, includesfirst metal layer 4 having a thickness of 200 nm formed on a top of bump7 of substrate 1, second layer 5 for preventing first metal layer 4 fromgrain boundary diffusion of Al atoms occurring in vertical to thesubstrate, and third layer 6 for adjusting a thickness of electrode 302.Diffusion-preventing layer 8 is formed on each side of electrode 302 toprevent first metal layer 4 from the grain boundary diffusion of the Alatoms. As shown in FIG. 23, diffusion-preventing layer 8 does not reacha bottom of the substrate, but covers each side of first metal layer 4,second layer 5, third layer 6, and a part of each side of bump 7 ofsubstrate 1.

Electrodes of comparative examples 7 to 10 have structures identical tothose of examples 13 and 14 illustrated by FIG. 21.

Table 7 shows materials of the layers, thicknesses of the layers, andmethods of forming the layers of the electrodes of examples 13 to 18 andcomparative examples 7 to 10.

TABLE 7 Number Bump of Method of Section of Substrate Base First SecondThird Forming of Layers (nm) Layer Layer Layer Layer Layers ElectrodeExample 13 3 — Material — *AlMg Ti AlMg IBS FIG. 21 Thickness — 200 20240 Example 14 3 — Material — *AlMg Cu AlMg IBS Thickness — 200 20 210Example 15 4 — Material Ti *AlMg Ti AlMg DCMS FIG. 22 Thickness 10 20020 230 Example 16 4 — Material Ti *AlMg Cu AlMg DCMS Thickness 10 200 20200 Example 17 3 10 Material — *AlMg Ti AlMg DCMS FIG. 23 Thickness —200 20 180 Example 18 3 10 Material — *AlMg Cu AlMg DCMS Thickness — 20010 150 Comparative 3 — Material — AlMg Ti AlMg DCMS FIG. 21 Example 7Thickness — 200 20 250 Comparative 3 — Material — AlMg Cu AlMg DCMSExample 8 Thickness — 200 20 220 Comparative 3 — Material — *AlMg TiAlMg IBS Example 9 Thickness — 300 20 160 Comparative 3 — Material —*AlMg Cu AlMg IBS Example 10 Thickness — 300 20 260 IBS: Ion beamsputtering DCMS: DC magnetron sputtering Asterisk “*” in the “material”column denotes a (111)-oriented layer. All the thicknesses are in nm.

As shown in Table 7, an AlMg alloy is used as metal of layer 4consisting of Al or consisting mainly of Al in the fourth embodiment,and Ti is used for the base layer. Ti is used for the second layers ofexamples 13, 15, and 17, and comparative examples 7 and 9, while Cu isused for the second layers of examples 14, 16, and 18 and comparativeexamples 8 and 10. The layers are formed by either ion beam sputteringor DC magnetron sputtering. Having the electrode layers formed, theelectrodes were examined by a θ−2θ X-ray diffraction method to determineorientation of the electrodes. Regarding the orientation of the AlMglayers of examples 13 to 18 and comparative examples 9 and 10, only a(111) peak of Al was observed, and thus the Al alloy layers are verifiedto be layers having a (111)-orientation in vertical to the substrate.Since each electrode includes two AlMg layers, that is, the first layerand the third layer, another sample having two layers, that is, a baselayer and a first layer was prepared under the same conditions of thelayer formation for the determination of the orientation. Forcomparative examples 7 and 8, no peak was observed from a specifiedcrystal plane, and thus the layers of the samples are not verified to beoriented layers, but non-oriented polycrystalline layers. The filters ofembodiment 4 have structure and design to those of embodiment 3. Theelectrodes are patterned by Ar⁺ ion milling. In the ion milling, sincethe patterning is physically carried out through sputtering, somesputtered atoms adhere to a side of the electrode, thus enabling thediffusion-preventing layer to be formed simultaneously to thepatterning. However, the diffusion-preventing layer does not cover theentire side of the electrode, thus not reaching a bottom of thesubstrate.

Table 8 shows an estimated live time of a SAW filter having eachelectrode shown in Table 7. Table 8 also shows crystal grain sizes ofthe respective AlMg layers, the first layers of the electrodes.

TABLE 8 Crystal Estimated Crystal Estimated Grain Life Grain Life Size(nm) Time (hrs) Size (nm) time (hrs) Example 200 58,000 Comparative 20014 13 Example 7 Example 200 63,000 Comparative 200 170 14 Example 8Example 200 85,000 Comparative 300 120 15 Example 9 Example 200 100,000Comparative 300 1200 16 Example 10 Example 200 85,000 17 Example 200100,000 18 The crystal grain size represents the crystal grain size ofthe first layer.

As shown in Table 8, the SAW filter each including the electrodes ofexamples 13 to 18 have the estimated life time exceeding 50,000 hours(the criteria), while the filter of comparative examples 7 to 10 has theestimated life time less than 50,000 hours. The AlMg layer, the firstlayer of each electrode has the crystal grain size substantially thesame as a thickness of the layer. After the test, in examples 13 and 14and comparative examples, a side hillock was at a side of the combelectrode besides a degraded portion of the electrode. The side hillockis formed between the substrate and the diffusion-preventing layer oneach side of the electrode to prevent the first metal layer from thegrain boundary diffusion of the Al atoms. Examples 15 to 18 had nodegradation of the electrode except for a degraded portion of theelectrode. This shows that the grain boundary diffusion of the Al atomsthrough each side of the electrode is restrained with the diffusionpreventing layer covering the part of the base layer or the part of eachside of the bump of the substrate and covering the entire first metallayer.

The filters each including the second layer of Ti has larger resistanceagainst an electric power than the filters each including the secondlayer of Cu. Since Cu has a diffusion coefficient to Al larger than aself-diffusion coefficient of Al, Cu atoms diffuse along grainboundaries in the second layer at a heating process in a manufacturingprocess for the filter, thereby obstructing a path of the grain boundarydiffusion of Al atoms. For this reason, the grain boundary diffusion ofthe Al atoms in horizontal direction to the substrate is restrained. Cueasily diffuses easily into Al, and further, easily forms metalliccompound with Al, and has the grain size grow in the second layer.Therefore, a change in temperature during the process and a thickness ofthe Cu layer influence an effect of restraining the Al atoms. Aresistance of the electrode layer easily increases. Thus the filtershave characteristics and resistance against an electric power andcharacteristics ranging widely.

The second layer containing the metal having the larger diffusioncoefficient to Al than the self-diffusion coefficient of Al having largeresistance against an electric power. The layer has an optimumthickness, thus requiring the manufacturing process, particularly theheating process to be controlled. If the thickness of the first metallayer consisting of Al or consisting mainly of Al is 200 nm or less, thethickness of the second layer of Cu is preferably 20 nm or less, morepreferably 10 nm or less. Moreover, the heating process is carried outpreferably at 250° C. or less, more preferably at 200° C. or less.

The second layer containing metal having a diffusion coefficient to Alsmaller than the self-diffusion coefficient of Al is expected to be lesseffective for restraining the grain boundary diffusion of the Al atomsin the first metal layer consisting of Al or consisting mainly of Althat occurs in horizontal to the substrate, but enables the filter tohave stabile resistance against an electric power and stablecharacteristics.

These facts show that the diffusion-preventing layer covering eachentire side of the first layer effectively restrains the grain boundarydiffusion of the Al atoms of the first metal layer consisting of Al orconsisting mainly of Al that occurs in horizontal to the substrate. Thediffusion-preventing layer may be formed by the patterning carried outthrough sputtering etching. The base layer or the bump formed bygrinding the substrate is effective. The diffusion-preventing layerformed on each side of the electrode by the method naturally become alaminated layer or an alloy layer with the first metal layer consistingof Al or consisting mainly of Al and either the base layer or thematerial of the substrate, thus having large resistance againstmigration

(Exemplary Embodiment 5)

FIGS. 24 to 26 are sections of electrodes which are essential parts ofrespective SAW filters of examples 19 to 23 in accordance with exemplaryembodiment 5. FIG. 27 is a section of an electrode of a SAW filter ofcomparative Example 11.

Each electrode 312 of examples 19 and 20, as shown in FIG. 24, includesfirst metal layer 4 of a 200 nm thickness on a top of bump 7 ofsubstrate 1, second layer 5 for preventing the first metal layer fromgrain boundary diffusion of Al atoms occurring in vertical to thesubstrate, and third layer 6 for adjusting a thickness of electrode 312.After the electrode is patterned, protective layer 9 is formed overelectrode 312. Protective layer 9 of example 19 is made of siliconnitride and has a thickness of 100 nm, while protective layer 9 ofexample 20 is made of silicon oxide and has a thickness of 100 nm.According to an observation with an electron microscope, the protectivelayer was not formed about the bump of the substrate, specifically abouta boundary between the comb electrode and a bottom of the substratebetween the electrodes, thus being discontinuously formed, as shown inFIG. 24.

Each electrode 322 of examples 21 and 22, as shown in FIG. 25, includesbase layer 3, first metal layer 4 having a 200 nm-thickness, secondlayer 5, and third layer 6 that are stacked in this order over substrate1. Second layer 5 prevents the first layer from grain boundary diffusionof Al atoms occurring in vertical to the substrate, while third layer 6adjusts a thickness of electrode 322. After electrode 322 is formed,protective layer 9 is formed over electrode 322. Protective layer 9 ofexample 21 is made of silicon nitride and has a thickness of 100 nm,while protective layer 9 of example 22 is made of silicon oxide and hasa thickness of 100 nm. According to an observation with an electronmicroscope, protective layer 9 was not formed about a boundary betweenbase layer 3 and a bottom of substrate 1, as shown in FIG. 25.

Electrode 332 of example 23, as shown in FIG. 26, includes base layer 3,first metal layer 4 of a 200 nm-thickness, second layer 5, and thirdlayer 6 that are stacked in this order over substrate 1. Second layer 5prevents the first metal layer from grain boundary diffusion of Al atomsoccurring in vertical to the substrate, while third layer 6 adjusts athickness of electrode 332. After electrode 332 is formed, siliconnitride layer 9 a of a 50 nm-thickness and silicon oxide layer 9 b of 50nm-thickness are formed over electrode 332. According to an observationwith an electron microscope, protective layers 9 a and 9 b are notformed about a boundary between base layer 3 and a bottom of substrate1, as shown in FIG. 26.

Electrode 342 of comparative example 11, as shown in FIG. 27, includesfirst metal layer 4 of a 200 nm-thickness, second layer 5 for preventingthe first metal layer from grain boundary diffusion of Al atomsoccurring in vertical to the substrate, and third layer 6 for adjustinga thickness of electrode 342. After the electrode is formed, protectivelayer 9 of a 100 nm-thickness made of silicon nitride is formed overelectrode 342. According to an observation with an electron microscope,protective layer 9 was not formed about a boundary between electrode 342and a bottom of substrate 1, as shown in FIG. 27.

Table 9 shows materials of the layers, thicknesses of the layers, andmethods of forming the layers of the electrodes of examples 19 to 23 andcomparative example 11.

TABLE 9 Number Bump of Pro- Method of Section of Substrate Base FirstSecond Third tective Forming of Layers (nm) Layer Layer Layer LayerLayer Layers Electrode Example 19 3 10 Material — *AlMg Ti AlMg SiliconIBS FIG. 27 Nitride Thickness — 200 20 140 100 Example 20 3 10 Material— *AlMg Ti AlMg Silicon IBS Oxide Thickness — 200 20 140 100 Example 214 — Material Ti *AlMg Ti AlMg Silicon DCMS FIG. 28 Nitride Thickness 10200 20 190 100 Example 22 4 — Material Ti *AlMg Ti AlMg Silicon DCMSOxide Thickness 10 200 20 190 100 Example 23 4 — Material Ti *AlMg TiAlMg Silicon DCMS FIG. 29 Oxide/ Silicon Nitride Thickness 10 200 20 19050/50 Com- 3 — Material — *AlMg Ti AlMg Silicon IBS FIG. 30 parativeNitride Example Thickness — 200 20 210 100 11 IBS: Ion beam sputteringDCMS: DC magnetron sputtering The asterisk “*” in the “material” columndenotes a (111)-oriented layer. All the thicknesses are in nm.

As shown in Table 9, an AlMg alloy is used as the metal consisting of Alor consisting mainly of Al in embodiment 5, and Ti is used for baselayers 3 and second layers 5. The layers are formed by either ion beamsputtering or DC magnetron sputtering. Having the electrode layersformed the electrodes were examined by a θ−2θ X-ray diffraction methodto determine orientation. Regarding the orientation of the AlMg layersof examples 19 to 23 and comparative example 11, only a (111) peak of Alwas observed. Thus, it is verified that the Al alloy layer is a(111)-orientation in vertical to the substrate. Since each sampleincludes two AlMg layers, that are the first layer and the third layer,another sample having a first layer and a still another sample having abase layer and a first layer are made under the same conditions of thelayer formation for determination of their orientation. The filters ofthe present embodiment have structures identical to those of the firstembodiment. The filter is provided with the Al electrode having athickness of 480 nm to have a center frequency of about 800 MHz. Theelectrodes are formed by photolithography and dry etching. After theelectrodes are formed, a protective layer is formed. And a portion ofthe protective layer for electrical connection is then removed byetching, and a resulting resonator is mounted on an alumina substrate toface down toward the substrate. In the present embodiment, the filtersare not hermetically sealed. The filters of this embodiment areevaluated in the same manner as in the first embodiment in respectiveresistances against electric power. The filters, which include theprotective layers, are evaluated while having their respective surfacesexposed to atmospheric air. Table 10 shows an estimated life time ofeach SAW filter having the electrodes shown in Table 9. Table 10 alsoshows crystal grain sizes of the AlMg layers (the first layers) of theelectrodes.

TABLE 10 Crystal Estimated Crystal Estimated Grain Life Grain Life Size(nm) Time (hrs) Size (nm) Time (hrs) Example 200 60,000 Comparative 200320 19 Example 11 Example 200 65,000 20 Example 200 60,000 21 Example200 65,000 22 Example 200 65,000 23 The crystal grain size representsthe crystal grain size of the first layer.

As shown in Table 10, the SAW filters including the respectiveelectrodes of examples 19 to 23 have the estimated life time exceeding50,000 hours (a criteria), while the filter of comparative example 11has the estimated life of less than 50,000 hours. The AlMg layer (thefirst layer) of each electrode has the crystal grain size substantiallythe same as a thickness of the electrode. It is apparent that thefilters of examples 19 and 21 each provided with the protective layer ofsilicon oxide have improved resistance against electric power ascompared with the filters of examples 20 and 22 each provided with theprotective layer of silicon nitride. It was observed that the filtershave electric characteristics slightly degraded after they have theprotective layer of silicon nitride formed, while the filters have nochanges in electric characteristics even after they have the protectivelayer of silicon oxide formed. The filter of example 23 including thelaminated protective layer of silicon nitride and silicon oxideexhibited no change in electric characteristics even after the filterhad the protective layers formed. It was observed that the filter had animproved resistance against electric power that was similar to that ofthe filter including only the silicon nitride. Although the filter ofcomparative example 11 has an electrode structure identical to that ofexample 13 of embodiment 4 and to have an excellent resistance againstelectric power, the filter has a short estimated life of 320 hours.Conceivably, this is because the filters are not hermetically sealed inembodiment 5. The filters of examples 19 to 23 exhibit substantially thesame level of resistance against electric power as the filtershermetically sealed. It is conceivable from this fact that the filter ofcomparative example 11 has the short life time since its first metallayer consisting of Al or consisting mainly of Al is partially exposed,not being entirely covered by the protective layer. The protective layereasily has a discontinuous portion as shown in each of FIGS. 25 to 27about a boundary between the electrode and a bottom of the substratewhere the protective: layer on the electrodes is thin. If such adiscontinuous portion is formed, it is apparent that the bump to thesubstrate or the base metal layer having excellent moisture resistancein the present embodiment is effective for extending the life time ofthe filter.

The protective layer prevents the electrode from a hillock caused bymigration of the Al atoms, thus improving the resistance againstelectric power, preventing the electrodes from a short circuit betweenthem, and improving moisture resistance.

In embodiment 5, the electrode is constructed to have the resistanceagainst electric power and the moisture resistance due to the protectivelayer. The protective layer on the electrode provided with the bump atthe substrate or the base layer having the excellent moisture resistanceis effective for extending the life time of the filter.

In embodiments 1 to 5, the structures of the electrodes for specifiedfilters are described. However, the present invention is not limited tothe structures, the thicknesses, the materials and others of the layersdescribed in the embodiments. In particular, the thickness of the layerconsisting of Al or consisting mainly of Al is preferably 0.01·L orless, where L is a width of the electrode of the SAW filter. Thus,conductive powder can be sufficiently fine, whereby stress on theelectrode that is caused by propagation of surface acoustic waves can besufficiently dispersed.

INDUSTRIAL APPLICABILITY

The present invention provides a surface acoustic wave filter havingimproved resistance against stress caused by propagation of surfaceacoustic waves, and a method of manufacturing the filter.

1. A surface acoustic wave (SAW) filter comprising: a substrate; and anelectrode provided over said substrate, said electrode comprising: afirst layer having a thickness of 200 nm or less, said first layer beingan oriented layer having a given orientation with respect with saidsubstrate, said first layer being made of metal including Al, a secondlayer on said first layer, said second layer preventing said first layerfrom grain boundary diffusion, said second layer being made of metal,said first layer being located between said substrate and said secondlayer, and a third layer on said second layer, said third layeradjusting a thickness of said electrode.
 2. The SAW filter of claim 1,wherein said metal including Al is one of Al and an alloy of Al and atleast one of Mg, Zr, Cu, Sc, Ti, and Ta.
 3. The SAW filter of claim 1,wherein said grain-boundary-diffusion preventing layer is made ofmaterial including metal having a diffusion coefficient into Al smallerthan a self-diffusion coefficient of Al.
 4. The SAW filter of claim 3,wherein said metal having said diffusion coefficient into Al smallerthan said self-diffusion coefficient of Al is one of TI, Ta, W, and Cr.5. The SAW filter of claim 1, further comprising: a protective layercovering at least a portion of said electrode.
 6. The SAW filter ofclaim 5, wherein said protective layer contains silicon nitride.
 7. TheSAW filter of claim 5, wherein said protective layer comprises alaminated layer including a layer of silicon nitride and a layer ofsilicon oxide.
 8. The SAW filter of claim 5, wherein said protectivelayer contains silicon oxide.
 9. A surface acoustic wave SAW filtercomprising: a substrate; an electrode provided over said substrate, saidelectrode comprising a first layer having a thickness of 200 nm or less,said first layer being an oriented layer having a given orientation withrespect with said substrate, said first layer being made of metalincluding Al; and a grain-boundary-diffusion-preventing layer providedon said electrode and made of metal, said electrode being locatedbetween said substrate and said grain-boundary-diffusion-preventinglayer; wherein said grain-boundary-diffusion-preventing layer is made ofmaterial including metal having a diffusion coefficient into Al largerthan a self-diffusion coefficient of Al.
 10. The SAW filter of claim 9,wherein said metal having said diffusion coefficient into Al larger thansaid self-diffusion coefficient of Al is one of Cu, Pd, and Mg.
 11. Asurface acoustic wave (SAW) filter comprising: a substrate; an electrodeprovided over said substrate, said electrode comprising a first layerhaving a thickness of 200 nm or less, said first layer being an orientedlayer having a given orientation with respect with said substrate, saidfirst layer being made of metal including Al; agrain-boundary-diffusion-preventing layer provided on said electrode andmade of metal, said electrode being located between said substrate andsaid grain-boundary-diffusion-preventing layer; and anAl-atom-diffusion-preventing layer provided on a side of said electrode.12. The SAW filter of claim 11, wherein saidAl-atom-diffusion-preventing layer covers a side of said first layer.13. A method of manufacturing a surface acoustic wave filter, comprisingthe steps of: forming an electrode over a substrate, the electrodeincluding a layer of metal including Al; and forming at least a portionof an Al-diffusion-preventing layer on a side of the electrode bysputter etching simultaneously to the forming of the electrode.
 14. Asurface acoustic wave (SAW) filter comprising: a substrate; and anelectrode provided over said substrate, said electrode comprising afirst layer having a thickness of 200 nm or less, said first layer beingan oriented layer having a given orientation with respect with saidsubstrate, wherein said substrate comprises a bump, and said electrodeis provided on a top of said bump.
 15. A surface acoustic wave SAWfilter comprising: a substrate; an electrode provided over saidsubstrate, said electrode comprising a first layer having a thickness of200 nm or less, said first layer being an oriented layer having a givenorientation with respect with said substrate, said first layer beingmade of metal including Al; and a grain-boundary-diffusion-preventinglayer provided on said electrode and made of metal, said electrode beinglocated between said substrate and saidgrain-boundary-diffusion-preventing layer; wherein said substratecomprises a bump, and said electrode is provided on a top of said bump.16. The SAW filter of claim 15, further comprising: anAl-atom-diffusion-preventing layer provided on a side of said electrode.17. The SAW filter of claim 16, wherein saidAl-atom-diffusion-preventing layer covers a side of said first layer.18. The SAW filter of claim 17, wherein saidAl-atom-diffusion-preventing layer covers at least a portion of a sideof said bump.
 19. The SAW filter of claim 15, further comprising: aprotective layer covering at least a portion of said electrode.
 20. TheSAW filter of claim 19, wherein said protective layer contains siliconoxide.
 21. The SAW filter of claim 19, wherein said protective layercovers at least a portion of a side of said bump.
 22. The SAW filter ofclaim 19, wherein said protective layer contains silicon nitride. 23.The SAW filter of claim 19, wherein said protective layer comprises alaminated layer including a layer of silicon nitride and a layer ofsilicon oxide.
 24. A surface acoustic wave SAW filter comprising: asubstrate; an electrode provided over said substrate, said electrodecomprising a first layer having a thickness of 200 nm or less, saidfirst layer being an oriented layer having a given orientation withrespect with said substrate, said first layer being made of metalincluding Al; and a grain-boundary-diffusion-Preventing layer providedon said electrode and made of metal, said electrode being locatedbetween said substrate and said grain-boundary-diffusion-preventinglayer, and a base layer provided between said substrate and said firstlayer; and an Al-atom-diffusion-preventing layer provided on a side ofsaid electrode.
 25. The SAW filter of claim 24, wherein saidAl-atom-diffusion-preventing layer covers a side of said first layer.26. The SAW filter of claim 25, wherein saidAl-atom-diffusion-preventing layer covers at least a portion of a sideof said base layer.
 27. The SAW filter of claim 24, further comprising:a protective layer covering at least a portion of said electrode. 28.The SAW filter of claim 27, wherein said protective layer containssilicon oxide.
 29. The SAW filter of claim 27, wherein said protectivelayer covers at least a portion of a side of said base layer.
 30. TheSAW filter of claim 27, wherein said protective layer contains siliconnitride.
 31. The SAW filter of claim 27, wherein said protective layercomprises a laminated layer including a layer of silicon nitride and alayer of silicon oxide.
 32. A surface acoustic wave (SAW) filtercomprising: a substrate; an electrode provided over said substrate, saidelectrode comprising a first layer having a thickness of 200 nm or less,said first layer being an oriented layer having a given orientation withrespect with said substrate, said first layer being made of metalincluding Al; and an Al-atom-diffusion-preventing layer provided on aside of said electrode, said Al-atom-diffusion-preventing layer beingmade of metal.
 33. The SAW filter of claim 32, wherein said metalincluding Al is one of Al and an alloy of Al and at least one of Mg, Zr,Cu, Sc, Ti, and Ta.
 34. The SAW filter of claim 32, wherein saidelectrode further comprises a second layer on said first layer, saidsecond layer preventing said first layer from grain boundary diffusion.35. The SAW filter of claim 34, wherein said electrode further comprisesa third layer on said second layer, said third layer adjusting athickness of said electrode.
 36. The SAW filter of claim 32, furthercomprising: a grain-boundary-diffusion-preventing layer provided on saidelectrode.
 37. The SAW filter of claim 36, wherein saidgrain-boundary-diffusion preventing layer is made of material includingmetal having a diffusion coefficient into Al smaller than aself-diffusion coefficient of Al.
 38. The SAW filter of claim 37,wherein said metal having said diffusion coefficient into Al smallerthan said self-diffusion coefficient of Al is one of Ti, Ta, W, and Cr.39. The SAW filter of claim 36, wherein saidgrain-boundary-diffusion-preventing layer is made of material includingmetal having a diffusion coefficient into Al larger than aself-diffusion coefficient of Al.
 40. The SAW filter of claim 39,wherein said metal having said diffusion coefficient into Al larger thansaid self-diffusion coefficient of Al is one of Cu, Pd, and Mg.
 41. TheSAW filter of claim 32, wherein said Al-atom-diffusion-preventing layercovers a side of said first layer.
 42. The SAW filter of claim 32,further comprising: a protective layer covering at least a portion ofsaid electrode.
 43. The SAW filter of claim 42, wherein said protectivelayer contains silicon nitride.
 44. The SAW filter of claim 42, whereinsaid protective layer comprises a laminated layer including a layer ofsilicon nitride and a layer of silicon oxide.
 45. The SAW filter ofclaim 42, wherein said protective layer contains silicon oxide.
 46. TheSAW filter of claim 32, wherein said substrate comprises a bump, andsaid electrode is provided on a top of said bump.
 47. The SAW filter ofclaim 46, wherein said Al-atom-diffusion-preventing layer covers a sideof said first layer.
 48. The SAW filter of claim 47, wherein saidAl-atom-diffusion-preventing layer covers at least a portion of a sideof said bump.
 49. The SAW filter of claim 46, further comprising: aprotective layer covering at least a portion of said electrode.
 50. TheSAW filter of claim 49, wherein said protective layer covers at least aportion of a side of said bump.
 51. The SAW filter of claim 49, whereinsaid protective layer contains silicon nitride.
 52. The SAW filter ofclaim 49, wherein said protective layer comprises a laminated layerincluding a layer of silicon nitride and a layer of silicon oxide. 53.The SAW filter of claim 49, wherein said protective layer containssilicon oxide.
 54. The SAW filter of claim 32, wherein said electrodefurther comprises a base layer provided between said substrate and saidfirst layer.
 55. The SAW filter of claim 54, wherein saidAl-atom-diffusion-preventing layer covers a side of said first layer.56. The SAW filter of claim 55, wherein saidAl-atom-diffusion-preventing layer covers at least a portion of a sideof said base layer.
 57. The SAW filter of claim 54, further comprising:a protective layer covering at least a portion of said electrode. 58.The SAW filter of claim 57, wherein said protective layer covers atleast a portion of a side of said base layer.
 59. The SAW filter ofclaim 57, wherein said protective layer contains silicon nitride. 60.The SAW filter of claim 57, wherein said protective layer comprises alaminated layer including a layer of silicon nitride and a layer ofsilicon oxide.
 61. The SAW filter of claim 57, wherein said protectivelayer contains silicon oxide.